JP7708965B2 - Capacity recovery method for lithium-ion secondary batteries - Google Patents

Description

The present invention relates to the field of lithium ion secondary batteries, and more specifically to a method for restoring the capacity of a lithium ion secondary battery and a lithium ion secondary battery obtained by this method.

In recent years, as the application range of lithium-ion secondary batteries (also known as "lithium ion batteries") becomes wider and wider, lithium-ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. However, as lithium-ion secondary batteries are used repeatedly, their capacity gradually decreases, affecting their service life and safety. At present, in-depth research on the capacity recovery of lithium-ion secondary batteries with capacity decay is still lacking.

The object of the present invention is to provide a method for recovering the capacity of a lithium-ion secondary battery with high efficiency and accuracy using a capacity recovery agent that does not remain in large amounts inside the secondary battery and ensures cycle stability for subsequent use of the secondary battery.

In order to achieve the above object, a first aspect of the present application provides a method for recovering capacity of a lithium ion secondary battery, the method comprising:
(1) providing a lithium ion battery having a faded capacity;
(2) providing a capacity recovery agent comprising lithium iodide and an organic solvent, the organic solvent being used to dissolve the lithium iodide;
(3) injecting the capacity recovery agent into the lithium ion battery whose capacity has been reduced;
(4) reacting the capacity recovery agent inside the lithium ion battery;
(5) pouring out the liquid mixture inside the lithium ion battery after the reaction, and injecting an electrolyte into the lithium ion battery.

Therefore, the present application effectively restores the capacity of a lithium-ion secondary battery by using a specific type of capacity recovery agent and replacing the electrolyte with a new one after the capacity recovery agent has reacted, while ensuring the cycle stability of the secondary battery for subsequent use.

In any embodiment, in the step (1), the capacity-faded lithium ion secondary battery is an active lithium-faded battery, and the capacity that needs to be restored for the capacity-faded lithium ion battery is C, and the method of calculating C is:
C=C2+C3−C1,
Here, C2=C1/(1-P1), where:
P1 is the active lithium loss rate of the capacity-faded lithium ion battery;
C1 is the discharge capacity of the present state of the capacity-faded lithium ion battery;
C2 is the discharge capacity corresponding to the positive electrode material activity of the lithium ion battery maximally accommodating lithium;
C3 is the capacity that needs to be charged before the capacity of the lithium ion battery that has been reduced in capacity is restored,
The above capacities are all calculated in Ah.

This allows the capacity that needs to be restored in the lithium-ion secondary battery to be accurately calculated, thereby providing targeted and precise adjustment and control over the capacity recovery of the lithium-ion secondary battery.

In any embodiment, the active lithium loss rate P1 of the capacity-degraded lithium ion battery is 5% or more. This allows the method of the present invention to be used to restore capacity to a lithium ion secondary battery.

In any embodiment, in the step (2), the mass m of lithium iodide added in the capacity recovery agent and the capacity C that needs to be restored in the lithium ion battery whose capacity has been reduced are expressed as follows:
m=C*M*1000/(n*M _li *3860), where
M represents the relative molecular mass of lithium iodide, g/mol;
n represents the number of lithium atoms in lithium iodide,
_M represents the relative atomic mass of the Li atom, g/mol;
3860 is the gram capacity of lithium metal, mAh/g.

This allows the mass of lithium iodide required to be accurately calculated, thereby precisely controlling the recovery capacity of the lithium-ion secondary battery.

In any embodiment, the content of the lithium iodide in the capacity recovery agent in step (2) is 0.5-15 wt %, optionally 0.5-6 wt %, calculated based on the total mass of the capacity recovery agent. Thereby, the lithium iodide of the specific content in the capacity recovery agent reacts better with the electrode plates inside the battery, thereby recovering the capacity of the lithium ion secondary battery.

In any embodiment, in step (2), the organic solvent includes a cyclic carbonate and a low viscosity solvent. This allows the specific combination of the organic solvent to better dissolve lithium iodide, thereby restoring the capacity of the lithium ion secondary battery.

In any embodiment, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC) or a combination thereof, and the content of the cyclic carbonate is 10-30% by weight, calculated based on the total mass of the organic solvent. Thereby, the cyclic carbonate has a high dielectric constant, and can ensure that lithium iodide has a relatively large solubility in the organic solvent.

In any embodiment, the low-viscosity solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, tetrahydrofuran, and 1,3-dioxolane, and the content of the low-viscosity solvent is 70-90% by weight, calculated based on the mass of the organic solvent. Thus, a specific type and content of low-viscosity solvent can alleviate the excessively high viscosity of the cyclic carbonate, and sufficiently infiltrate the inside of the battery, thereby ensuring the capacity recovery of the lithium-ion secondary battery.

In any embodiment, in step (4), the capacity recovery agent is reacted inside the lithium ion secondary battery by leaving the battery at 20-60°C. Under the reaction conditions, the capacity recovery agent sufficiently infiltrates the inside of the lithium ion secondary battery, ensuring the capacity recovery of the lithium ion secondary battery.

In any of the embodiments, in step (4), the capacity recovery agent can be reacted inside the lithium ion battery by ultrasonic waves or heating. This can accelerate the infiltration of the capacity recovery agent into the electrodes inside the lithium ion secondary battery, accelerating the reaction rate and improving the efficiency of capacity recovery of the secondary battery.

In any embodiment, in step (5), after the liquid mixture inside the lithium ion secondary battery after the reaction is poured out, an organic cleaning agent is injected to clean the battery, the battery is vacuum dried, and finally an electrolyte is injected into the lithium ion battery. This prevents the capacity recovery agent from remaining inside the battery, and ensures the cycle stability and safety of the lithium ion secondary battery after capacity recovery.

A second aspect of the present application provides a lithium ion secondary battery, which is a lithium ion secondary battery obtained by the method according to the first aspect of the present application, wherein the positive electrode active material of the lithium ion secondary battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a lithium-containing phosphate having an olivine structure, and optionally
The lithium-containing phosphate having an olivine structure is characterized in that it is at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

A third aspect of the present application provides a battery module, which includes a secondary battery according to the second aspect of the present application.

A fourth aspect of the present application provides a battery pack, which includes a battery module according to the third aspect of the present application.

A fifth aspect of the present application provides a power consumption device, which includes at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

This application adds a capacity recovery agent containing lithium iodide to a lithium ion secondary battery whose capacity has been reduced, thereby replenishing active lithium to the positive electrode plate inside the lithium ion secondary battery and activating the inactive lithium in the negative electrode, thereby ensuring highly efficient and accurate control of the capacity recovery of the lithium ion secondary battery, and replacing the electrolyte with a new one after the capacity recovery agent reacts, thereby eliminating the effect of the capacity recovery agent on the safety and cycle stability of the subsequent operation of the lithium ion secondary battery.

1 is a flow chart of a method according to one preferred embodiment of the present application.

Hereinafter, with appropriate reference to the drawings, a detailed description will be given of the embodiments specifically disclosing the capacity recovery method for a lithium ion secondary battery, the corresponding secondary battery, the battery module, the battery pack and the electrical device of the present application. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicate description of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to allow those skilled in the art to easily understand. Note that the drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisaged. However, if 1 and 2 are listed as minimum range values, and 3, 4, and 5 are listed as maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisaged. In this application, unless otherwise specified, a numerical range "a-b" represents a shorthand representation of any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" represents a list of all real numbers between "0-5" already listed in this specification, and "0-5" is just a shorthand for combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise stated, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

Unless otherwise stated, all technical features and optional technical features of this application may be combined with each other to form a new technical solution.

Unless otherwise stated, all steps in this application may be performed in sequence or randomly, and are preferably performed in sequence. For example, the method includes steps (a) and (b) to mean that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, the method mentioned above may further include step (c) to mean that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

Unless otherwise specified, the terms "comprise" and "include" referred to in this application may be open ended or closed ended. For example, the terms "comprise" and "include" may further include or include other components not listed, or may include or include only the components listed.

Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied in the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); and A and B are both true (or exist).

At present, lithium ion secondary batteries are widely used in various fields, and the usage is huge, which causes the capacity to gradually fade due to repeated charging and discharging during use. Most of the conventional technical solutions all add lithium supplementary additives to the battery core of a fresh battery to make the initial active lithium content of the battery core relatively high, but do not mention the recovery of the battery after the capacity fades. For the capacity recovery of a secondary battery with faded capacity, the research of those skilled in the art is very limited, and only mentions that a capacity recovery agent can be added to a secondary battery with faded capacity, but the capacity recovery degree is limited and accurate capacity recovery adjustment and control cannot be realized, and the capacity recovery agent still exists in the electrolyte system after the capacity is recovered, which affects the cycle stability of the battery core in the later stage. The inventor has found through a large amount of research that the method of the first aspect of the present invention can accurately recover the capacity of a lithium ion secondary battery with high efficiency by precisely controlling the addition of a specific type and content of capacity recovery agent and replacing the electrolyte, and the capacity recovery agent does not remain inside the secondary battery, ensuring the cycle stability of the secondary battery in subsequent use.

METHOD FOR CAPACITY RECOVERY OF LITHIUM ION SECONDARY BATTERY In one embodiment of the present application, referring to FIG. 1, the present application provides a method for capacity recovery of a lithium ion secondary battery, which includes:
(1) providing a lithium ion battery having a faded capacity;
(2) providing a capacity recovery agent comprising lithium iodide and an organic solvent, the organic solvent being used to dissolve the lithium iodide;
(3) injecting the capacity recovery agent into the lithium ion battery whose capacity has been reduced;
(4) reacting the capacity recovery agent inside the lithium ion battery;
(5) pouring out the liquid mixture inside the lithium ion battery after the reaction, and injecting an electrolyte into the lithium ion battery.

Although the mechanism is not yet clear, the applicant unexpectedly discovered that the present application uses a capacity recovery agent containing lithium iodide, and replaces the electrolyte with a new one after the capacity recovery agent reacts, thereby effectively recovering the capacity of the lithium ion secondary battery and ensuring the cycle stability of the secondary battery in the subsequent use. Specifically, taking a lithium iron phosphate-based lithium ion secondary battery as an example, lithium iodide reacts with iron phosphate in the delithiated positive electrode to generate lithium iron phosphate and triiodide ion (I ₃ ^- ),
2Li ^{++ 3I-} + _2FePO4 = _2LiFePO4 + _I3- ^,
During this reaction, the lithium in the lithium iodide enters the positive electrode through an oxidation-reduction reaction as an additional lithium source, increasing the total amount of available active lithium inside the secondary battery.

At the same time, at the negative electrode, triiodide ions (I ₃ ⁻ ) can react with non-active lithium (lithium oxide in the SEI film (solid electrolyte interfacial film) and lithium precipitated from the negative electrode surface) to generate soluble LiI;
3Li ₂ O+3I ₃ ⁻ =6Li ⁺ +IO ₃ ⁻ +8I ⁻ ,
Soluble LiI can also react with _FePO4 at the positive electrode to produce _LiFePO4 ,
2Li+I ₃ ⁻ =2Li ⁺ 3I ⁻ ,
This therefore achieves the activation of inactive lithium, thereby achieving the capacity recovery of the secondary battery.

The term "active lithium" refers to lithium ions that can participate in redox reactions occurring during charging and discharging in a battery.

In some embodiments, in the step (1), the capacity-faded lithium ion secondary battery is an active lithium faded battery, and the capacity that needs to be restored for the capacity-faded lithium ion battery is C, and the method of calculating C includes:
C=C2+C3−C1,
Here, C2=C1/(1-P1),
Where:
P1 is the active lithium loss rate of the capacity-faded lithium ion battery;
C1 is the discharge capacity of the present state of the capacity-faded lithium ion battery;
C2 is the discharge capacity corresponding to the positive electrode material activity of the lithium ion battery maximally accommodating lithium;
C3 is the capacity that needs to be charged before the capacity of the lithium ion battery that has been reduced in capacity is restored,
The above capacities are all calculated in Ah.

This allows the capacity that needs to be restored in the lithium-ion secondary battery to be accurately calculated, thereby providing targeted and precise adjustment and control over the capacity recovery of the lithium-ion secondary battery.

The "active lithium decay battery" is a secondary battery in which the active lithium in the positive electrode gradually decreases after the initial formation and/or during use.

The method for calculating the active lithium loss rate P1 of the capacity-faded lithium ion secondary battery is as follows:
Active lithium loss rate P1=(C20-C10)/C20;
where C10 is the capacity corresponding to the present state of active lithium of the 154.025 ^mm2 battery cathode, and C20 is the capacity corresponding to the accommodated active lithium of the 154.025 ^mm2 battery cathode.

The test methods for C10 and C20 are as follows:

The negative electrode plate of the fully discharged battery is taken, and the negative electrode plate is punched into a circular sheet having an area of 154.025 ^mm2 using a sheet punching machine _, to manufacture a lithium button battery with the negative electrode. The button battery is charged, and the charging flow is recorded as C10, as shown in Table 1. The button battery is discharged and then charged, and the recharge capacity is recorded as C20, as shown in Table 2 (wherein the loss of active lithium due to the loss of the negative electrode active material is not taken into account). Here, the _U1 and _U2 values of different lithium ion secondary batteries are referred to Table 3.

When the secondary battery is in a fully discharged state and undergoes capacity recovery, C3 is 0 Ah and C = C2 - C1.

In some embodiments, the active lithium loss rate P1 of the capacity-faded lithium ion secondary battery is 5% or more. This allows the method of the present invention to be used to restore capacity to the lithium ion secondary battery.

In some embodiments, in the step (2), the mass m of lithium iodide added in the capacity recovery agent and the capacity C that needs to be restored in the lithium ion battery whose capacity has been reduced are
m=C*M*1000/(n*M _li *3860), where
M represents the relative molecular mass of lithium iodide, g/mol;
n represents the number of lithium atoms in lithium iodide,
_M represents the relative atomic mass of the Li atom, g/mol;
3860 is the gram capacity of lithium metal, mAh/g.

This allows the mass of lithium iodide required to be accurately calculated, thereby precisely controlling the recovery capacity of the lithium-ion secondary battery.

In some embodiments, the content of lithium iodide in the capacity recovery agent is 0.5-15 wt%, optionally 0.5-6 wt%, calculated based on the total mass of the capacity recovery agent. Thereby, a certain content of lithium iodide in the capacity recovery agent reacts better with the electrode plate inside the battery, thereby recovering the capacity of the lithium ion secondary battery. When the capacity to be recovered of the lithium ion secondary battery is constant, the lower the concentration of lithium iodide in the capacity recovery agent, the greater the total amount of capacity recovery agent required. Therefore, it is difficult for the concentration of lithium iodide to be lower than 0.5 wt%. At the same time, the higher the concentration of lithium iodide, the greater the viscosity of the solvent recovery agent, which makes it difficult for the capacity recovery agent to diffuse on the electrode plate, and the capacity recovery effect of the negative electrode plate is distributed unevenly, and thus the center of the electrode plate cannot react with the capacity recovery agent and cannot recover the capacity. Therefore, it is difficult for the concentration of lithium iodide to be higher than 15 wt%.

In some embodiments, in step (2), the organic solvent includes a cyclic carbonate and a low-viscosity solvent. The cyclic carbonate has a high dielectric constant and can ensure that lithium iodide has a relatively large solubility in the organic solvent, so that even if a small amount of the capacity recovery agent is added, the expected capacity recovery effect can be achieved. However, the cyclic carbonate has a relatively high viscosity, which affects the diffusion of the capacity recovery agent between the plates, making the middle position of the plate not very well infiltrated and unable to participate in the reaction, or reducing the reaction time between the middle position and the solvent recovery agent, making the middle of the plate not very well activated. At this time, a low-viscosity solvent is added to reduce the viscosity of the system and ensure that the plate is fully infiltrated, thereby ensuring that the plate is fully activated.

In some embodiments, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC) or a combination thereof, preferably ethylene carbonate, and the content of the cyclic carbonate is 10-30% by weight, preferably 20-30% by weight, calculated based on the total mass of the organic solvent. Thereby, the specific type of cyclic carbonate can further ensure that lithium iodide has a relatively large solubility in the organic solvent, so that the expected capacity recovery effect can be achieved even with the addition of a small amount of the capacity recovery agent.

In some embodiments, the low-viscosity solvent is one or more of dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, tetrahydrofuran, and 1,3-dioxolane, preferably dimethyl carbonate, and the content of the low-viscosity solvent is 70-90% by weight, preferably 70-80% by weight, calculated based on the mass of the organic solvent. Thereby, the specific type and content of the low-viscosity solvent can alleviate the excessively high viscosity of the cyclic carbonate, sufficiently infiltrate the inside of the battery, and thereby ensure the capacity recovery of the lithium-ion secondary battery.

In some embodiments, in step (3), the capacity recovery agent is injected into the lithium ion battery whose capacity has faded. The electrolyte in the battery may be drained before injecting the capacity recovery agent, or the capacity recovery agent may be directly injected without draining the electrolyte. Preferably, the electrolyte in the battery is drained before injecting the capacity recovery agent. Those skilled in the art should be aware that when the capacity fade of the lithium ion battery is serious, the free electrolyte remaining in the battery is very small, and at this time, the capacity recovery agent can be directly injected into the battery. The capacity recovery agent can be injected in any manner known to those skilled in the art, for example, by injection with a syringe.

In some embodiments, in step (4), the capacity recovery agent is reacted inside the lithium ion battery by standing at a temperature of 20-60°C, preferably 20-45°C. Typically, the standing time is 24-72 hours, preferably 45-55 hours. Under the reaction conditions, the capacity recovery agent sufficiently infiltrates the inside of the lithium ion secondary battery, ensuring the capacity recovery of the lithium ion secondary battery.

In some embodiments, in step (4), the capacity recovery agent can be reacted inside the lithium ion secondary battery by ultrasonic waves or heating. In some embodiments, ultrasonic waves can be applied at a frequency of 25 KHz-80 KHz, preferably 30-50 KHz, for 2-4 h, preferably 2 h, to accelerate the reaction of the capacity recovery agent inside the lithium ion secondary battery. In some embodiments, heating can be performed in an oven at 20-45°C for 1-4 h to accelerate the reaction of the capacity recovery agent inside the lithium ion secondary battery. This can accelerate the infiltration of the capacity recovery agent into the electrodes inside the lithium ion secondary battery, accelerating the reaction rate and improving the efficiency of capacity recovery of the secondary battery.

In some embodiments, in step (5), after the liquid mixture inside the lithium ion battery after the reaction is poured out, an organic cleaning agent is injected to clean the lithium ion battery, the battery is vacuum dried, and finally an electrolyte is injected into the lithium ion battery. This prevents the capacity recovery agent from remaining inside the battery, and ensures the cycle stability and safety of the lithium ion secondary battery after capacity recovery.

In some embodiments, the organic cleaner is the same as the low viscosity solvent, preferably DMC. After cleaning with the organic cleaner, the secondary battery is vacuum dried, typically at 20-45°C, preferably at room temperature, at a vacuum of -0.08 to -0.1 MPa. Typically, the vacuum drying is performed for 0.2-1 hour, preferably 0.5 hour.

In some embodiments, by implementing the method of the present application, the capacity recovery rate of a lithium-ion secondary battery is 0.5%-15%.

The capacity recovery rate P of the secondary battery is
It is calculated by the formula P = (Ca - Cb) / Cb * 100%,
Where:
Cb is the discharge capacity of the battery before capacity recovery, calculated based on Ah;
Ca is the discharge capacity of the battery after capacity recovery, calculated based on Ah.

The test methods for Ca and Cb are as follows:

At 25°C, the lithium ion secondary battery is charged to _U10 at a constant current of 0.04C, left for 5 min, and then discharged to _U20 at 0.04C, and the resulting discharge capacity is recorded as the initial discharge capacity C0, where the values of _U10 and _U20 refer to Table 4.

The above steps are repeated three times for the same battery, and the discharge capacity Cn of the battery after the nth step is recorded at the same time. The average value of the three discharge capacities is taken as the discharge capacity Cb of the battery before capacity recovery. After the capacity of the battery is restored, the above charge/discharge flow is repeated three times, and the average value of the three discharge capacities is taken as the discharge capacity Ca of the battery after capacity recovery.

The test method for the current capacity C1 of the lithium ion secondary battery whose capacity has been reduced is the same as the test method for Cb.

A second aspect of the present application provides a lithium ion secondary battery, which is a lithium ion secondary battery obtained by the method according to the first aspect of the present application, wherein the positive electrode active material of the lithium ion secondary battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a lithium-containing phosphate having an olivine structure, and optionally
The lithium-containing phosphate having an olivine structure is characterized in that it is at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During charging and discharging of the battery, active ions are absorbed and released back and forth between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is installed between the positive electrode plate and the negative electrode plate, and mainly functions to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through.

[Positive electrode plate]
The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present application.

For example, the positive electrode current collector has two opposing surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on one or both of the two opposing surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, an aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material can be any positive electrode active material known in the art for use in batteries. For example, the positive electrode active material may be a lithium cobalt oxide (e.g., LiCoO ₂ ), a lithium nickel oxide (e.g., LiNiO ₂ ), a lithium manganese oxide (e.g., LiMnO ₂ , LiMn ₂ O ₄ ), a lithium nickel cobalt oxide, a lithium manganese cobalt oxide, a lithium nickel manganese oxide, a lithium nickel cobalt manganese oxide (e.g., LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (which may be abbreviated as NCM333), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (which may be abbreviated as NCM523), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (which may be abbreviated as NCM211), LiNi _0.6 Co _0.2 Mn _{0.2 ... (} may be abbreviated as NCM622), _{LiNi0.8Co0.1Mn0.1O2} (may be abbreviated _{as NCM811} ), lithium nickel cobalt aluminum oxide (e.g., _{LiNi0.85Co0.15Al0.05O2} ), and lithium-containing phosphates having an olivine structure, and optionally the lithium-containing phosphates having an olivine structure are lithium iron phosphate (e.g., _LiFePO4 (may _{be abbreviated as} LFP)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., _LiMnPO4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon, but is not limited thereto. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more.

In some embodiments, the positive electrode membrane layer further optionally includes an adhesive. By way of example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further comprises a conductive agent. By way of example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode plate can be manufactured in the following manner. The components for manufacturing the positive electrode plate, such as the positive electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then coated onto a positive electrode current collector, and the positive electrode plate is obtained after processes such as drying and cold pressing.

[Negative electrode plate]
The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on one or both of the two opposing surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, the metal foil sheet may be a copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer . The composite current collector may be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode active material may be a negative electrode active material used in batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may be selected from at least one of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy. The tin-based material may be selected from at least one of a tin element, a tin oxide, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode membrane layer further optionally includes an adhesive. The adhesive may be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode membrane layer optionally further comprises other additives, such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

In some embodiments, the negative electrode plate can be manufactured in the following manner. The components for manufacturing the negative electrode plate, such as the negative electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then coated onto a negative electrode current collector, and the negative electrode plate is obtained after processes such as drying and cold pressing.

[Electrolyte]
The electrolyte serves to conduct ions between the positive and negative electrodes. The present application is not specifically limited to the type of electrolyte, which can be selected according to need. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte solution further optionally includes additives. For example, the additives may include an anode film-forming additive, a cathode film-forming additive, and may further include additives that can improve some performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[Separator]
In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of separator, and any known porous structure separator having good chemical stability and mechanical stability may be selected.

In some embodiments, the separator material may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single layer film or a multilayer composite film, with no particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, with no particular limitation.

In some embodiments, the positive and negative electrodes and the separator can be fabricated into an electrode assembly by a winding or stacking process.

In some embodiments, the secondary battery may include an exterior body. The exterior body may be used to package the electrode assembly and electrolyte.

In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate. A preferred exterior of the secondary battery is a pouch.

This application is not particularly limited to the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape.

In some embodiments, the secondary battery product of different shapes includes a housing and the secondary battery of the present invention packaged in the housing. The housing may include a case and a cover plate. Here, the case may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case has an opening communicating with the receiving cavity, and the cover plate can cover the opening to seal the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly by a winding process or a stacking process. An electrolyte is infiltrated into the electrode assembly to form the secondary battery cell of the present invention. The secondary battery cell is packaged in the receiving cavity. The number of secondary battery cells included in the secondary battery may be one or more, and can be specifically selected by those skilled in the art according to actual needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, with the specific number being selectable by one skilled in the art depending on the application and capacity of the battery module.

In the battery module, the multiple secondary batteries may be arranged in sequence along the longitudinal direction of the battery module. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries may be secured in place by fasteners.

Optionally, the battery module may further include a housing having an accommodation space, and the multiple secondary batteries are accommodated in the accommodation space.

In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, with the specific number being selectable by one skilled in the art depending on the application and capacity of the battery pack.

The battery pack may include a battery box and a plurality of battery modules installed in the battery box. The battery box may include an upper housing and a lower housing, and the upper housing may cover the lower housing to form an enclosed space for accommodating the battery modules. The plurality of battery modules may be arranged in the battery box in any manner.

The present application further provides a power consumption device, the power consumption device including at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device, or may be used as an energy storage unit for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

The power consumption device can be selected as a secondary battery, a battery module, or a battery pack depending on the usage demand.

The power consumer may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the demand for high power and high energy density of the secondary battery of the power consumer, a battery pack or battery module may be employed.

Other example devices may be mobile phones, tablet computers, notebook computers, etc. These devices generally require a thin design and may employ secondary batteries as a power source.

Examples The following are examples of the present application. The examples described below are illustrative and are only for interpreting the present application, and should not be understood as limitations on the present application. In the examples, unless specific techniques or conditions are specified, the techniques, conditions or products described in the literature in the field are followed. Unless the manufacturer is specified, the reagents or instruments used are all ordinary products that can be obtained from the market.

Example 1
(1) Taking a lithium iron phosphate secondary battery with a capacity fade, the active lithium loss rate P1 of the secondary battery is measured to be 20% according to the method described in the specification, and the discharge capacity C1 of the battery in its current state is measured to be 116mAh. The tested battery core is in a fully discharged state, that is, the capacity C3 that needs to be charged before the battery capacity is restored is 0. Then, the capacity C that needs to be restored of the lithium iron phosphate battery with a capacity fade is calculated to be 29mAh according to the following formula:
C=C2+C3−C1,
Here, C2=C1/(1-P1),
Where:
P1 is the active lithium loss rate of the capacity-faded lithium iron phosphate battery;
C1 is the discharge capacity of the present state of the lithium iron phosphate battery whose capacity has been faded;
C2 is the discharge capacity of the lithium iron phosphate battery when the positive electrode material is capable of maximally accommodating active lithium;
C3 is the capacity that needs to be charged before the capacity of the lithium iron phosphate battery that has been reduced in capacity is restored,
The above capacities are all calculated based on Ah.
(2) Calculate the mass m of lithium iodide to be added based on the capacity C required to be restored of the lithium iron phosphate battery obtained in step (1) to be 0.146 g;
m=C*M*1000/(n*M _li *3860), where,
M represents the relative molecular mass of lithium iodide, g/mol;
n represents the number of lithium atoms in lithium iodide,
_M represents the relative atomic mass of the Li atom, g/mol;
The 3860 represented the gram capacity of lithium metal, mAh/g.

Dissolving the amount of lithium iodide in 14.6 g of a mixed solvent of ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7 to provide a capacity recovery agent;
(3) Using a tool, one corner of the battery core of the pouched lithium iron phosphate battery is sheared, and the electrolyte is poured out. Then, using a syringe, 10 g of the capacity recovery agent obtained in step (2) is injected into the battery core of the lithium ion secondary battery. Then, using a heat sealer, the battery core is sealed, and the packaging conditions are 140° C., 10 s.

(4) The battery core is left at rest at 25° C. for 48 hours to allow the capacity recovery agent to react inside the lithium iron phosphate battery.
(5) One corner of the battery core in step (4) was sheared, and the liquid mixture inside the lithium iron phosphate battery after the reaction was poured out. Then, 10 g of DMC was injected into the battery core, soaked for 30 min, and poured out. The above operation was repeated six times. Then, the battery core was dried at 25°C and a vacuum of -0.1 MPa for 30 min. Then, the electrolyte was injected into the battery core. Then, the battery core was sealed using a heat sealer, and the packaging conditions were 140°C and 10 s.

Example 2-18
Except for changing the type, mass and ratio of different solvents in the mixed solvent in the solvent recovery agent, the type of battery, the battery charge state before recovery and the reaction conditions, the same steps as in Example 1 were followed. The details are shown in Table 1.

Comparative Example 1
The same steps as in Example 1 were followed, except that the electrolyte was not poured out in step (3) and step (5) was not performed.

Comparative Example 2
The same steps as in Example 1 were followed, except that no lithium iodide was added.

Battery Performance Test The discharge capacities of the batteries after capacity recovery in the above Examples and Comparative Examples were tested before and after capacity recovery according to the method described in the specification, and the corresponding capacity recovery rates P were calculated. The results are shown in Table 2.

As can be seen from the above results, after the lithium ion secondary batteries of Examples 1-17 of the present invention were subjected to capacity recovery by the method of the present invention, the capacity recovery rates all reached an ideal range (all were 5% or more, and even reached 20% or more), and the cycle retention rates of the capacity-recovered batteries after 500 cycles at 25°C were still maintained at a relatively high level (80% or more).

In comparison, the capacity recovery agent of Comparative Example 1 was used directly after the reaction without pouring out the reaction mixture, resulting in a capacity recovery rate of 13%, but a cycle retention rate of only 80%, both of which are lower than those of the Examples. The capacity recovery agent of Comparative Example 2 does not contain lithium iodide, and after the battery is treated using the same method as the present invention, the battery capacity hardly changes and the effect of battery capacity recovery cannot be achieved.

Claims (12)

A method for recovering capacity of a lithium ion battery, comprising:
(1) providing a lithium ion battery having a faded capacity;
(2) providing a capacity recovery agent comprising lithium iodide and an organic solvent, the organic solvent being used to dissolve the lithium iodide;
(3) injecting the capacity recovery agent into the lithium ion battery whose capacity has been reduced;
(4) reacting the capacity recovery agent inside the lithium ion battery;
(5) A method for recovering the capacity of a lithium ion battery, comprising the steps of pouring out the liquid mixture inside the lithium ion battery after the reaction, and injecting an electrolyte into the lithium ion battery. In the step (1), the capacity-faded lithium ion secondary battery is an active lithium-faded battery, and the capacity that needs to be restored for the capacity-faded lithium ion battery is C, and the method of calculating C is as follows:
C=C2+C3−C1,
Here, C2=C1/(1-P1), where:
P1 is the active lithium loss rate of the capacity-faded lithium ion battery;
C1 is the discharge capacity of the present state of the capacity-faded lithium ion battery;
C2 is the discharge capacity corresponding to the positive electrode material activity of the lithium ion battery maximally accommodating lithium;
C3 is the capacity that needs to be charged before the capacity of the lithium ion battery that has been reduced in capacity is restored,
2. The method of claim 1, wherein each of said capacities is calculated in Ah. The method according to claim 1 or 2, characterized in that the active lithium loss rate P1 of the capacity-faded lithium ion battery is 5% or more. In the step (2), the mass m of lithium iodide added in the capacity recovery agent and the capacity C that needs to be restored in the lithium ion battery whose capacity has decreased are
m=C*M*1000/(n*M _li *3860), where
M represents the relative molecular mass of lithium iodide, g/mol;
n represents the number of lithium atoms in lithium iodide,
_M represents the relative atomic mass of the Li atom, g/mol;
3. The method of claim 2, wherein 3860 is the gram capacity of lithium metal, mAh/g. The method according to claim 1 or 2, characterized in that in the capacity recovery agent in step (2), the content of the lithium iodide is 0.5-15 wt% , calculated based on the total mass of the capacity recovery agent. The method according to claim 1 or 2, characterized in that in step (2), the organic solvent includes a cyclic carbonate and a low-viscosity solvent. 7. The method according to claim 6, wherein the cyclic carbonate is ethylene carbonate (EC) and/or propylene carbonate ( PC ), and the content of the cyclic carbonate is 10-30% by weight, calculated based on the mass of the organic solvent. The method according to claim 6, characterized in that the low-viscosity solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, tetrahydrofuran, and 1,3-dioxolane, and the content of the low-viscosity solvent is 70-90% by weight, calculated based on the total mass of the organic solvent. The method according to claim 1 or 2, characterized in that in step (4), the capacity recovery agent is reacted inside the lithium ion battery by leaving the battery at rest at 20-60°C. The method according to claim 8, characterized in that in step (4), the capacity recovery agent can be reacted inside the lithium ion battery by ultrasonic waves or heating. The method according to claim 1 or 2, characterized in that in step (5), after pouring out the liquid mixture inside the lithium ion battery after the reaction, an organic cleaning agent is injected to wash it, the battery is vacuum dried, and finally an electrolyte is injected into the lithium ion battery. 3. The method according to claim 1 , wherein the positive electrode active material of the lithium ion battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate having an olivine structure.